Revert r267126: "DevTools: handle Tracing.start in both browser and renderer" It was plain wrong.

content/browser/devtools/devtools_tracing_handler.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/devtools/devtools_tracing_handler.h"
 
 #include <cmath>
 
 #include "base/bind.h"
 #include "base/callback.h"
@@ skipping 151 matching lines @@
               base::IgnoreResult(&TracingController::GetTraceBufferPercentFull),
               base::Unretained(TracingController::GetInstance()),
               base::Bind(&DevToolsTracingHandler::OnBufferUsage,
                          weak_factory_.GetWeakPtr())),
           true));
       buffer_usage_poll_timer_->Reset();
     }
   }
 
   TracingController::GetInstance()->EnableRecording(
-      categories, options, TracingController::EnableRecordingDoneCallback());
+      categories, options,
+      base::Bind(&DevToolsTracingHandler::OnTracingStarted,
+                 weak_factory_.GetWeakPtr(),
+                 command));
 
-  return command->SuccessResponse(NULL);
+  return command->AsyncResponsePromise();
+}
+
+void DevToolsTracingHandler::OnTracingStarted(
+    scoped_refptr<DevToolsProtocol::Command> command) {
+  SendAsyncResponse(command->SuccessResponse(NULL));
 }
 
 void DevToolsTracingHandler::OnBufferUsage(float usage) {
   base::DictionaryValue* params = new base::DictionaryValue();
   params->SetDouble(devtools::Tracing::bufferUsage::kParamValue, usage);
   SendNotification(devtools::Tracing::bufferUsage::kName, params);
 }
 
 scoped_refptr<DevToolsProtocol::Response>
 DevToolsTracingHandler::OnEnd(
     scoped_refptr<DevToolsProtocol::Command> command) {
   buffer_usage_poll_timer_.reset();
   TracingController::GetInstance()->DisableRecording(
       base::FilePath(),
       base::Bind(&DevToolsTracingHandler::BeginReadingRecordingResult,
                  weak_factory_.GetWeakPtr()));
   return command->SuccessResponse(NULL);
 }
 
 }  // namespace content